Recently, projection type image display apparatuses (hereinafter, described also as projectors) have been widespread, and such projection type image display apparatuses often have been used in various locations indoors and outdoors, in addition to the conventional application in an environment with relatively clean air, such as a meeting room of an enterprise. The increased scope of the use location results in variation in the use environments, and thus the conditions for temperature, humidity and air cleanliness become more severe. As a result, with the expanding use, new problems have occurred with respect to the quality of the projector.
In particular, when the projection type image display apparatus is used in an environment with an inferior air cleanliness, dust and dirt enter the interior of the cabinet of the projector and adhere to elements and components of the optical system, thereby degrading drastically the illuminance of the projector. For solving the problem, a dustproof measure for a projector is an urgent and important technical object.
For a conventional dustproof measure in a projection type image display apparatus, an air filter is provided at an opening, and concurrently, a wall is provided on the interior of the display apparatus so as to configure a dustproof space in which optical components (prism unit) are housed (see Patent Document 1 for example). In this example, a buffer material as a dustproof member is inserted in the clearance of a dustproof space.
Dustproof measures for circuit boards are disclosed in Patent Documents 2 and 3, for example. The methods include: filling through holes of a printed wiring board for IC cards with plated metal so as to prevent dust and dirt from entering the substrate at the side where electronic components are mounted; or attaching a shield case to a substrate, thereby enveloping the substrate with the shield case and a metal case so as to prevent adherence of dust.